Bulkhead arrangement for a wind turbine blade

ABSTRACT

A bulkhead assembly for a wind turbine blade is described, wherein a pressure relief conduit is provided at the bulkhead to allow for pressure to equalise across the bulkhead. This helps to prevent faults or cracks in the bulkhead assembly due to differences in pressure on either side of the bulkhead. Furthermore, liquid traps and/or filter media can be accommodated in the conduit to prevent the passage of liquids or other matter across the bulkhead.

FIELD OF THE INVENTION

The present invention relates to a bulkhead arrangement for a windturbine blade.

BACKGROUND OF THE INVENTION

Wind turbine blades are often provided with a bulkhead arranged at theroot end of the blade. The bulkhead is generally used to provide a workplatform for workers carrying out maintenance or repair on the blade,and to prevent internal debris and fluids such as water or oil frompassing between the internal blade cavity and the wind turbine rotor huband machine housing.

The bulkhead may be flexibly mounted to the internal wall of the windturbine blade using a flexible mounting flange, an example of which canbe seen in WO 2012/119934. Alternatively, the bulkhead may be rigidlymounted to the internal wall. A sealing member may be located around theperiphery of the bulkhead, to ensure that the bulkhead is watertight.

One issue with such current wind turbine blade bulkhead arrangements isthat cracks or faults may be observed in the mounting flanges and/orsealing members over time, thereby compromising the integrity of thebulkhead mounting and the effectiveness of the sealing properties of thebulkhead. It is thought that such faults are the result of centrifugalforces acting on the flanges and/or sealing members, blade deformationsdue to wind loads, and pressure differentials between opposed sides ofthe bulkhead.

Such cracks or faults must be repaired to ensure operationaleffectiveness of the wind turbine. The current approach to mitigatingsuch problems is the construction of stronger mounting flanges and/orsealing members, resulting in an increase in blade costs and/or weight.

Accordingly, it is an object of the invention to provide a bulkheadsystem for a wind turbine blade having improved resistance tooperational defects such as crack or fault formation in the bulkheadmounting flanges and/or sealing members.

SUMMARY OF THE INVENTION

Accordingly, there is provided a wind turbine blade comprising:

-   -   a sealed bulkhead provided in said wind turbine blade; and    -   at least one pressure relief conduit having a first open end        located at a first side of said bulkhead and a second open end        located at a second side of said bulkhead,    -   wherein said pressure relief conduit is operable to equalize the        pressure difference between said first side and said second side        of said bulkhead.

By providing a pressure relief conduit in fluid communication betweeneither side of a blade bulkhead, the strain on the bulkhead, and inparticular on the joint between the bulkhead and the body of the windturbine blade, can be reduced by avoiding a pressure difference acrossthe bulkhead.

It will be understood that the wind turbine blade comprises a blade bodyhaving an outer blade shell defining an internal blade cavity. It willbe understood that the bulkhead may be provided within said blade cavityto divide an internal cavity of the wind turbine blade into separateportions. Furthermore, it will be understood that the bulkhead maypreferably be provided at or on the root end of the wind turbine blade.

It will also be understood that the bulkhead may comprise at least onesealable access opening. Such a sealable access opening can beunderstood as an access hatch or door providing passage through saidbulkhead, which is closed an sealed during normal use of the windturbine blade, the access opening having a diameter suitable for thepassage of a worker. The at least one sealable access opening isunderstood to be distinct from said at least one pressure reliefconduit, where preferably the diameter of said pressure relief conduitis less than 10 centimetres.

In one aspect of the invention, the at least one pressure relief conduitmay comprise a bore defined in the body of said bulkhead, said boreextending from the first side of said bulkhead to the second side ofsaid bulkhead.

Additionally or alternatively, the at least one pressure relief conduitcomprises a tube or pipe extending through the body of said bulkhead.

Additionally or alternatively, at least one pressure relief conduit isarranged adjacent said bulkhead.

In one aspect, said at least one pressure relief conduit is providedbetween said bulkhead and the blade body or outer blade shell of saidwind turbine blade.

In an additional or alternative aspect of the invention, said bulkheadis secured to the blade body via a sealing flange provided about theperiphery of said bulkhead, said sealing flange located between saidbulkhead and said blade body, wherein said at least one pressure reliefconduit extends through said sealing flange, adjacent to said bulkhead.

It will be understood that the sealing flange may comprise at least oneflexible member arranged around the periphery of the bulkhead.

In an alternative aspect, said at least one pressure relief conduit isprovided in the blade body or outer blade shell of said wind turbineblade.

In such an embodiment, said at least one pressure relief conduit isprovided as a tube or conduit embedded into the wall of the blade body,having first and second open ends located at opposed sides of saidbulkhead. Such a tube or conduit may be arranged in the wall of theblade body during manufacture of the blade shell, e.g. during fibrelay-up of a shell for a wind turbine blade.

Preferably, said at least one pressure relief conduit comprises at leastone liquid trap.

It will be understood that said at least one liquid trap may comprise aU-bend, a J-bend, or an S-bend trap in said conduit.

In one aspect of the invention said at least one conduit is provided ina curved arrangement, wherein at least one of said first or second endsextends back in the direction of the opposed second or first end of theconduit.

Such an arrangement acts to provide a simple liquid trap for theconduit, preventing the ease that moisture may enter the conduit.

Additionally or alternatively, said at least one liquid trap maycomprise a filter material located within said conduit.

Said filter material may comprise a permeable sponge, a permeablemembrane, or any suitable material arranged to allow the passage ofgases and vapours through said conduit and to prevent the passage offluids such as water, oil, etc., and/or debris such a dirt, dust, wastematerial, etc. through the conduit.

It will be understood that the at least one pressure relief conduit maybe formed from a flexible tube. Additionally or alternatively, the atleast one conduit may be formed from pre-formed or moulded piping. Theconduit may be formed from a C-shaped, S-shaped, U-shaped, or J-shapedpiece of tubing or piping.

In a preferred aspect of the invention, there is provided a wind turbineblade having a blade body defining an internal cavity, the wind turbineblade comprising:

-   -   a bulkhead provided in said internal cavity; and    -   a bulkhead valve located at said bulkhead, the bulkhead valve        extending from a first end located at a first side of said        bulkhead and a second end located at a second side of said        bulkhead,    -   wherein said bulkhead valve comprises a pressure relief conduit        extending between said first end and said second end, said        pressure relief conduit formed to have at least one liquid trap        between said first end and said second end.

The valve acts to relieve pressure on either side of bulkhead, while theliquid trap prevents the passage or moisture and/or dirt or debrisacross the bulkhead. Preferably, the wind turbine blade comprises ablade root wherein said bulkhead is located at or on the blade root.

In a further aspect of the invention, said at least one pressure reliefconduit is formed from a first pressure release tube having a first openend and a second closed end, and a second pressure release tube having afirst open end and a second end,

-   -   wherein the first open end of said pressure relief conduit is        formed by the first open end of said first pressure release        tube,    -   wherein the second open end of said pressure relief conduit is        formed by the first open end of said second pressure release        tube, and    -   wherein said first and second pressure relief tubes are        communicatively coupled via an outlet channel extending between        said first and second pressure relief tubes,    -   wherein said outlet channel is arranged on said first pressure        relief tube at a point between the first and second ends of said        first pressure relief tube.

By spacing the outlet channel from the second closed end of the firstpressure relief tube, a simple liquid trap is created between the firstand second pressure relief tubes.

Preferably, said second pressure release tube comprises a second closedend opposed to said first open end, wherein said outlet channel isarranged on said second pressure relief tube at a point between thefirst and second ends of said second pressure relief tube.

Preferably, at least one of said first and second pressure relief tubescomprises a curved section to form at least one liquid trap between therespective first and second ends.

Preferably, at least one of said first and second pressure relief tubescomprises a J-shaped tube.

There is further provided a bulkhead for a wind turbine blade, thebulkhead having at least one pressure relief conduit having a first endlocated at a first side of said bulkhead and a second end located at asecond side of said bulkhead,

-   -   wherein said pressure relief conduit is operable to equalize the        pressure difference between said first side and said second side        of said bulkhead when the bulkhead is installed in or on a wind        turbine blade.

In one aspect, said at least one pressure relief conduit extends throughthe body of said bulkhead. In an additional or alternative aspect, saidat least one pressure relief conduit is provided adjacent the body ofsaid bulkhead, preferably extending through a sealing flange providedabout the periphery of said bulkhead.

In a further aspect of the invention, the wind turbine blade comprises apressure relief conduit assembly, wherein the blade comprises at leastone end cap provided at one of said first or second open ends of said atleast one pressure relief conduit, said at least one end cap arranged tosubstantially seal said conduit at said first or second open end.

Preferably, at least one ventilation hole is defined in a wall of saidpressure relief conduit, further preferably wherein said at least oneventilation hole is provided adjacent said at least one end cap.

Preferably, said at least one cap comprises an end piece tosubstantially seal an open end of said conduit, said at least one endcap further comprising a collar depending from said end piece, saidcollar spaced from the wall of said pressure relief conduit, and actingto shield at least a portion of said at least one ventilation hole.

Preferably, said collar extends from a location adjacent an end of saidpressure relief conduit to a location along the longitudinal length ofsaid pressure relief conduit beyond the location of said at least oneventilation hole on said pressure relief conduit.

Preferably, said collar extends in a direction substantially parallel tothe wall of said pressure relief conduit.

Preferably, said collar extends in a direction flared away from the wallof said pressure relief conduit.

Preferably, said at least one end cap is arranged to be attached to saidbulkhead or to an internal wall of said wind turbine blade.

Preferably, said at least one end cap comprises at least one bolt lug.

Preferably, said at least one end cap is arranged such that a gap isdefined between an end of said collar and the attached bulkhead orinternal wall of the wind turbine blade.

Preferably, a first set of ventilation holes are defined in a wall ofsaid pressure relief conduit at a location adjacent said first open end,and wherein a second set of ventilation holes are defined in a wall ofsaid pressure relief conduit at a location adjacent said second openend.

Preferably, the wind turbine blade comprises a first end cap provided atsaid first open end of said pressure relief conduit and a second end capprovided at said second open end of said pressure relief conduit,wherein said first end cap acts to shield at least a portion of saidfirst set of ventilation holes and wherein said second end cap acts toshield at least a portion of said second set of ventilation holes.

There is also provided a method of manufacturing a wind turbine blade,the method comprising the steps of:

-   -   providing a wind turbine blade shell;    -   providing a bulkhead located on or in said wind turbine blade;        and    -   providing at least one pressure relief conduit having conduit        openings either side of said bulkhead, said pressure relief        conduit arranged to equalise the pressure difference across said        bulkhead.

In one aspect, said step of providing at least one pressure reliefconduit comprises providing a conduit which extends through saidbulkhead.

In an additional or alternative aspect, said step of providing at leastone pressure relief conduit comprises providing a conduit which islocated adjacent said bulkhead, preferably extending through a sealantmember or sealing flange provided around the periphery of said bulkheadbetween said bulkhead and said wind turbine blade shell.

In a further additional or alternative aspect, the method comprises thestep of:

-   -   embedding at least a portion of said pressure relief conduit in        a wall of said wind turbine blade shell, prior to a step of        installing said bulkhead in said wind turbine blade shell.

In one aspect, the step of providing a wind turbine blade shellcomprises the steps of laying up a fibre-based composite in a mould andcuring said fibre-based composite to form at least a portion of a windturbine blade shell, wherein said step of embedding comprisesincorporating at least a portion of said conduit in said blade wallduring said laying up process, e.g. moulding the conduit into the bladewall during a fibre lay-up process in a blade mould.

Preferably, the method comprises the steps of:

-   -   securing said pressure relief conduit to an internal surface of        said wind turbine blade shell, preferably adhering said pressure        relief conduit to said internal surface;    -   sealing said bulkhead in said wind turbine blade shell using a        sealing flange about the periphery of said bulkhead, wherein        said pressure relief conduit extends either side of said sealing        flange.

It will be understood that any of the above described features may becombined and implemented in a single embodiment without departing fromthe scope of the invention.

DESCRIPTION OF THE INVENTION

Embodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying drawings, in which:

FIG. 1 shows a side plan view of a wind turbine according to anembodiment of the invention comprising a de-icing array;

FIG. 2 shows the wind turbine of FIG. 1 when a wind turbine blade ispitched relative to the de-icing array;

FIG. 3 shows a cross-sectional view of a first embodiment of a bulkheadassembly according to the invention;

FIG. 4 shows a cross-sectional view of a second embodiment of a bulkheadassembly according to the invention;

FIG. 5 shows a cross-sectional view of a third embodiment of a bulkheadassembly according to the invention;

FIG. 6 shows a cross-sectional view of a fourth embodiment of a bulkheadassembly according to the invention;

FIG. 7 shows a side plan view and a cross-sectional view of a pressurerelief conduit assembly according to a further embodiment of theinvention;

FIG. 8( a) shows a side plan view and a cross-sectional view of an endcap of the assembly of FIG. 7;

FIG. 8( b) shows an isometric perspective view of a tube of the assemblyof FIG. 7;

FIG. 9 shows a top plan view, a side plan view, and a cross-sectionalview of an end cap of a pressure relief conduit assembly according to afurther embodiment of the invention; and

FIG. 10 shows an embodiment of a pressure relief conduit assembly in awinf turbine blade bulkhead according to an embodiment of the invention,incorporating the end cap of FIG. 9.

FIG. 1 illustrates a conventional modern upwind wind turbine accordingto the so-called “Danish concept” with a tower 4, a nacelle 6 and arotor with a substantially horizontal rotor shaft. The rotor includes ahub 8 and three blades 10 extending radially from the hub 8, each havinga blade root 16 nearest the hub and a blade tip 14 furthest from the hub8. The rotor has a radius denoted R.

FIG. 2 shows a schematic view of a first embodiment of a wind turbineblade 10 which may be used according to an embodiment of the invention.The wind turbine blade 10 has the shape of a conventional wind turbineblade and comprises a root region 30 closest to the hub, a profiled oran airfoil region 34 furthest away from the hub and a transition region32 between the root region 30 and the airfoil region 34. The blade 10comprises a leading edge 18 facing the direction of rotation of theblade 10, when the blade is mounted on the hub, and a trailing edge 20facing the opposite direction of the leading edge 18.

The airfoil region 34 (also called the profiled region) has an ideal oralmost ideal blade shape with respect to generating lift, whereas theroot region 30 due to structural considerations has a substantiallycircular or elliptical cross-section, which for instance makes it easierand safer to mount the blade 10 to the hub. The diameter (or the chord)of the root region 30 is typically constant along the entire root area30. The transition region 32 has a transitional profile 42 graduallychanging from the circular or elliptical shape of the root region 30 tothe airfoil profile 50, as shown in FIG. 3, of the airfoil region 34.The chord length of the transition region 32 typically increasessubstantially linearly with increasing distance r from the hub.

The airfoil region 34 has an airfoil profile 50 with a chord extendingbetween the leading edge 18 and the trailing edge 20 of the blade 10.The width of the chord decreases with increasing distance r from thehub.

It should be noted that the chords of different sections of the bladenormally do not lie in a common plane, since the blade may be twistedand/or curved (i.e. pre-bent), thus providing the chord plane with acorrespondingly twisted and/or curved course, this being most often thecase in order to compensate for the local velocity of the blade beingdependent on the radius from the hub.

Wind turbine blades are generally formed from fibre-reinforced plasticsmaterial, e.g.

glass fibres and/or carbon fibres which are arranged in a mould andcured with a resin to form a solid structure, in this case a shell toform a wind turbine blade 10. Modern wind turbine blades can often be inexcess of 30-40 metres in length, having blade root diameters of severalmetres.

The wind turbine further comprises a bulkhead 22 provided inside theshell of the wind turbine blade 10, which acts to seal the interior ofthe wind turbine blade 10. The bulkhead may be provided towards the rootend 16 of the wind turbine blade 10, preferably within the inboard 20%of the blade 10. It will be understood that the bulkhead 22 may beprovided at the substantially circular opening defined at the root end16, or may be spaced from the terminal point of the blade 10. Thebulkhead 22 may be rigidly secured to the internal wall of the windturbine blade shell 10, for example bolted or riveted, or the bulkhead22 may be connected to the wind turbine blade shell 10 via a relativelyflexible connection, e.g. a flexible flange member arranged around theperiphery of the bulkhead, which is coupled to the internal wall of theshell of the wind turbine blade 10. The bulkhead 22 may comprise anumber of access hatches or doors (not shown) to permit passage throughthe bulkhead 22. The bulkhead 22 is arranged to be substantiallywatertight during operation of the wind turbine, to prevent liquids ordebris passing between the interior of the blade 10 and the generalmachine housing of the rotor hub 8 and the nacelle 6.

The wind turbine further comprises a pressure relief conduit, which islocated at, on, or in said bulkhead 22, and which acts to relieve thepressure difference which may be experienced across the bulkhead 22. Byproviding such a conduit, the pressure difference across the bulkhead22, between a first side facing the interior of the wind turbine blade10 and a second side facing outwards from the root end 16 of the blade10, can be allowed to equalise. Accordingly, any damage or cracking tothe bulkhead 22 itself and/or to any mounting or sealing means used inthe wind turbine due to the existence of a pressure difference acrossthe bulkhead 22 can be prevented.

With reference to FIG. 3, a cross-sectional view of a section of abulkhead assembly according to an embodiment of the invention is shown.The bulkhead 22 comprises a first side 22 a and a second side 22 b. Athrough-going bore 24 is provided in the bulkhead 22 extending throughthe body of the bulkhead 22, between the first and second sides 22 a, 22b. A pressure relief conduit 26 is provided at said bore 24, the conduithaving a first open end 26 a located at the first side 22 a of saidbulkhead 22, and a second open end 26 b located at the second side 22 bof said bulkhead 22. The conduit 26 provides for gaseous communicationbetween the first and second sides 22 a, 22 b of the bulkhead 22, suchthat the pressure across the bulkhead 22 may be equalised.

In the embodiment of FIG. 3, the open ends 26 a, 26 b of the conduit 26stand proud of the surface of the body of the bulkhead 22, but is willbe understood that the ends 26 a, 26 b of the conduit 26 mayalternatively be provided flush with the surface of the bulkhead 22.

The pressure relief conduit 26 may further comprise a filter medium. Theembodiment of FIG. 3 comprises a mesh or sponge 28 located in theconduit 26, which is arranged to prevent the passage of debris throughthe conduit 26.

In a further aspect of the invention, the pressure relief conduit maycomprise at least one liquid trap located between the first and secondopen ends of the conduit.

A further embodiment of a bulkhead assembly according to the inventionis shown in FIG. 4. In this embodiment, the pressure relief conduit is ashaped piece of tubing 126 which extends through bore 24 of the bulkhead22, wherein the conduit 126 comprises a first liquid trap in the form ofa U-bend 130 a in the tubing, the first liquid trap located towards thefirst open end 126 a of the conduit 126, the conduit 126 furthercomprising a second liquid trap in the form of a U-bend 130 b in thetubing, the second liquid trap located towards the second open end 126 bof the conduit 126.

The presence of the liquid traps 130 a, 130 b towards the ends 126 a,126 b of the conduit 126 acts to restrict the entrance of liquids intothe conduit 126, where liquids may pass from the interior of the windturbine blade 10 to the machine housing of the wind turbine.

It will be understood that the at least one pressure relief conduit maybe formed from a flexible tube, or a section of pre-formed or mouldedpiping. It will be understood that the liquid trap may be formed by anysuitable shaping of the tubing forming the conduit, e.g. a C-shaped,S-shaped, U-shaped, or J-shaped piece of tubing or piping.

A further embodiment of the invention is illustrated in FIG. 5, where ashaped pressure relief conduit 226 similar to that shown in theembodiment of FIG. 4 is arranged adjacent a bulkhead 22, and does notextend through the bulkhead 22. In this embodiment, the edge of thebulkhead 22 is received within a sealing flange 32. The sealing flange32 extends about the periphery of the bulkhead 22, and is secured to theinternal surface of the wall 34 of the shell of the wind turbine blade10.

The pressure relief conduit 226 is arranged to extend through thesealing flange 32, such that the first and second open ends 226 a, 226 bof the conduit 226 are located at first and second sides 22 a, 22 b ofthe bulkhead 22 respectively.

Such a bulkhead assembly can be formed by providing a bore in thesealing flange 32, or by applying the sealing flange 32 around theconduit 226. In one aspect, the conduit 126 may be adhered to theinternal surface of the blade wall 34 before installation of the sealingflange 32 and the bulkhead 22.

One of the advantages of this embodiment is that a bore does not have tobe defined or formed in the body of the bulkhead 22. Accordingly, thestructural integrity of the bulkhead 22 can be preserved.

In a further aspect of the invention not shown, the conduit 226 may beembedded in the blade wall 34, having first and second open ends 226 a,226 b defined in the blade wall 34 at either side of the bulkhead 22.For such a case, a channel may be defined in the blade wall 34 toreceive the conduit 226. Alternatively, the conduit 226 may be formedwithin or incorporated into the blade wall 34 as part of themanufacturing process, e.g. the conduit 226 moulded into the blade wall34 during a fibre lay-up process in a blade mould.

A further embodiment of the invention is shown in FIG. 6, where thepressure relief conduit 326 is formed from a first tube 36 and a secondtube 38 in fluid communication with each other. The first tube 36comprises a first open end 36 a and a second closed end 36 b, and thesecond tube 38 comprises a first open end 38 a and a second closed end38 b. The first and second tubes 36,38 are substantially J-shaped tubes,wherein a liquid trap is formed in each tube by the shaping of the tubes36,38, the liquid traps located towards the first open ends 36 a, 38 aof the respective tubes 36,38.

The tubes 36,38 are arranged such that the first open end 36 a of thefirst tube 36 is located at the first side 22 a of the bulkhead 22, andthe second open end 38 a of the second tube 38 is located at the secondside 22 b of the bulkhead 22. In the embodiment shown in FIG. 6, afilter medium 40 comprising a mesh or sponge is provided in the firsttube 36, and the second tube 38 extends through the body of the bulkhead22, but it will be understood that any suitable arrangement of thecomponents of the bulkhead assembly may be used.

The first and second tubes 36,38 are positioned adjacent one another,and are communicatively coupled via an outlet channel 42 defined in thebody of the tubes 36,38. The outlet channel 42 is located on the firstand second tubes at a point between the first ends 36 a, 38 a and secondends 36 b, 38 b of the respective first and second tubes 36,38. Byspacing the outlet channel from the closed ends of the tubes, furtherliquid traps are created between the first and second pressure relieftubes.

A further embodiment of a pressure relief conduit assembly 400 for usein a wind turbine blade is indicated in FIGS. 6 and 7.

The pressure relief conduit assembly 400 comprises an open-ended tube402. A plurality of ventilation holes are defined in the wall of thetube 402. A first set of ventilation holes 404 a are defined near afirst end 402 a of the tube 402, with a second set of ventilation holes404 b defined near an opposed second end 402 b of the tube 402.

It will be understood the tube 402 may be positioned to extend through awind turbine blade bulkhead, or may be positioned to the side of abulkhead having said first and second ends 402 a, 402 b arranged oneither side of the bulkhead, similar to the constructions shown in theprevious embodiments. The tube 402 acts to equalise pressure across thebulkhead in the blade, providing a pressure release channel betweeneither side of the bulkhead.

The pressure relief conduit assembly 400 further comprises a pair of endcaps 406,408, fitted to respective first and second ends 402 a, 402 b ofthe tube 402. The end caps 406,408 comprise an end surface 406 a, 408 ahaving respective collars 406 b, 408 b depending therefrom.

The caps 406,408 are arranged such that the end surfaces 406 a, 408 asubstantially close the respective open ends 402 a, 402 b of the tube402. The collars 406 b, 408 b extend from the respective ends 402 a, 402b of the tube 402, to a location along the longitudinal length of thetube 402 beyond the location of the respective first and second sets ofventilation holes 404 a, 404 b. In this regard, the collars 406 b, 408 bact as a cover or shield over the exposed ventilation holes 404 a, 404 bdefined in the external wall of the tube 402.

The collars 406 b, 408 b are spaced from the external surface of thetube 402, such that a gap is preserved between the collars 406 b, 408 band the openings of the ventilation holes 404 a, 404 b. Accordingly, thearrangement of the collars 406 b, 408 b and the ventilation holes 404 a,404 b in the tube wall acts to impede ingress of dirt and debris intothe interior of the tube 402.

In the embodiment of FIGS. 7 and 8, the first and second caps 406,408are substantially identical. In a further embodiment, shown in FIGS. 9and 10, the pressure relief conduit assembly 400 comprises a third capdesign, indicated at 410.

In this embodiment, the second end cap 408 is replaced by a third endcap 410. The third cap 410 comprises an end section 410 a arranged tosubstantially seal the second open end 402 b of the tube 402, the thirdcap 410 further comprising a flared or umbrella-shaped collar 410 bdepending from said end section 410 a. As with the embodiment of FIGS. 7and 8, the flared collar 410 b is arranged to extend along the length ofthe tube 402 from the second end 402 b beyond the location of the secondset of ventilation holes 404 b.

The third cap 410 further comprises at least one lug 412 to receive abolt or other suitable securing device, the at least one lug 412 locatedat the free end of the flared collar 410 b. With reference to FIG. 10,the at least one lug 412 can be used to secure the third cap 410 to thesurface 22 a of a blade bulkhead 22, using a fastening device such as abolt or screw (not shown). Additionally or alternatively, it will beunderstood that the third cap 410 may be arranged to secure the pressurerelief conduit assembly to a surface of a blade wall.

As can be seen in FIG. 9, the at least one lug 412 is arranged toproject from the free end of the flared collar 410 b, such that when thethird cap 410 is secured to the surface of the bulkhead as shown in FIG.10, a gap 414 is defined between the bulkhead surface 22 a and the freeend of the flared collar 410 b. This embodiment allows for the pressurerelief conduit assembly to be relatively easily secured to the generalblade structure. While the third cap 410 shown in FIGS. 9 and 10comprises four separate lugs 412, it will be understood that any numberof and arrangement of lugs may be used. Additionally or alternatively,the third cap 410 may be secured to a bulkhead or to a blade wall usingan adhesive or other suitable securing method.

It will be understood that the end caps 406,408,410 may be fitted to theends of the tube 402 using any suitable method, e.g. a press fitting orsnap fitting arrangement, or the use of a suitable attachment devicesuch as a bolt, screw, staple, etc. or an adhesive. Furthermore, whilethe tube and end caps shown have a substantially circularcross-sectional profile, it will be understood that the elements of thepressure relief conduit may have other cross-sectional shapes, e.g.square, rectangular, etc.

Such a construction of a pressure relief conduit allows for relativelyeasy manufacture and assembly of the conduit for use in a wind turbineblade.

The invention provides a pressure relief conduit for a wind turbineblade bulkhead assembly, having conduit openings at either side of thebulkhead, such that the pressure difference can be equalised across thebulkhead, preventing faults or cracks in the bulkhead assembly due topressure differences. Liquid traps and/or filter media can beaccommodated in the conduit to prevent the passage of liquids or othermatter across the bulkhead.

The invention is not limited to the embodiment described herein, and maybe modified or adapted without departing from the scope of the presentinvention.

1. A wind turbine blade comprising: a sealed bulkhead provided in saidwind turbine blade; and at least one pressure relief conduit having afirst open end located at a first side of said bulkhead and a secondopen end located at a second side of said bulkhead, wherein saidpressure relief conduit is operable to equalize the pressure differencebetween said first side and said second side of said bulkhead.
 2. Thewind turbine blade of claim 1, wherein said at least one pressure reliefconduit comprises a bore defined in the body of said bulkhead, said boreextending from the first side of said bulkhead to the second side ofsaid bulkhead.
 3. The wind turbine blade of claim 1, wherein the atleast one pressure relief conduit comprises a tube or pipe extendingthrough the body of said bulkhead.
 4. The wind turbine blade of claim 1,wherein said at least one pressure relief conduit is arranged adjacentsaid bulkhead.
 5. The wind turbine blade of claim 4, wherein said atleast one pressure relief conduit is provided between said bulkhead andthe blade body or outer blade shell of said wind turbine blade.
 6. Thewind turbine blade of claim 4, wherein said bulkhead is secured to theblade body via a sealing flange provided about the periphery of saidbulkhead, said sealing flange located between said bulkhead and saidblade body, wherein said at least one pressure relief conduit extendsthrough said sealing flange, adjacent to said bulkhead.
 7. The windturbine blade of claim 6, wherein the sealing flange comprises at leastone flexible member arranged around the periphery of the bulkhead. 8.The wind turbine blade of claim 1, wherein said at least one pressurerelief conduit comprises at least one liquid trap.
 9. The wind turbineblade of claim 8, wherein said at least one liquid trap comprises atleast one of a U-bend, a J-bend, or an S-bend trap.
 10. The wind turbineblade of claim 1, wherein said at least one liquid trap comprises afilter material located within said conduit.
 11. The wind turbine bladeof claim 1, wherein the at least one pressure relief conduit is formedfrom a flexible tube.
 12. The wind turbine blade of claim 1, whereinsaid at least one pressure relief conduit is formed from a firstpressure release tube having a first open end and a second closed end,and a second pressure release tube having a first open end and a secondend, wherein the first open end of said pressure relief conduit isformed by the first open end of said first pressure release tube,wherein the second open end of said pressure relief conduit is formed bythe first open end of said second pressure release tube, and whereinsaid first and second pressure relief tubes are communicatively coupledvia an outlet channel extending between said first and second pressurerelief tubes, wherein said outlet channel is arranged on said firstpressure relief tube at a point between the first and second ends ofsaid first pressure relief tube.
 13. The wind turbine blade of claim 12,wherein said second pressure release tube comprises a second closed endopposed to said first open end, wherein said outlet channel is arrangedon said second pressure relief tube at a point between the first andsecond ends of said second pressure relief tube.
 14. The wind turbineblade of claim 1, wherein the wind turbine blade comprises a pressurerelief conduit assembly, wherein the blade comprises at least one endcap provided at one of said first or second open ends of said at leastone pressure relief conduit, said at least one end cap arranged tosubstantially seal said conduit at said first or second open end. 15.The wind turbine blade of claim 14, wherein at least one ventilationhole is defined in a wall of said pressure relief conduit, preferablywherein said at least one ventilation hole is provided adjacent said atleast one end cap.
 16. The wind turbine blade of claim 15, wherein saidat least one cap comprises an end piece to substantially seal an openend of said conduit, said at least one end cap further comprising acollar depending from said end piece, said collar spaced from the wallof said pressure relief conduit, and acting to shield at least a portionof said at least one ventilation hole.
 17. The wind turbine blade ofclaim 16, wherein said collar extends from a location adjacent an end ofsaid pressure relief conduit to a location along the longitudinal lengthof said pressure relief conduit beyond the location of said at least oneventilation hole on said pressure relief conduit.
 18. The wind turbineblade of claim 16, wherein said collar extends in a directionsubstantially parallel to the wall of said pressure relief conduit. 19.The wind turbine blade of claim 16, wherein said collar extends in adirection flared away from the wall of said pressure relief conduit. 20.The wind turbine blade of claim 14, wherein said at least one end cap isarranged to be attached to said bulkhead or to an internal wall of saidwind turbine blade.
 21. The wind turbine blade of claim 20, wherein saidat least one end cap comprises at least one bolt lug.
 22. The windturbine blade of claim 20, wherein said at least one end cap is arrangedsuch that a gap is defined between an end of said collar and theattached bulkhead or internal wall of the wind turbine blade.
 23. Thewind turbine blade of claim 14, wherein a first set of ventilation holesare defined in a wall of said pressure relief conduit at a locationadjacent said first open end, and wherein a second set of ventilationholes are defined in a wall of said pressure relief conduit at alocation adjacent said second open end.
 24. The wind turbine blade ofclaim 23, wherein the wind turbine blade comprises a first end capprovided at said first open end of said pressure relief conduit and asecond end cap provided at said second open end of said pressure reliefconduit, wherein said first end cap acts to shield at least a portion ofsaid first set of ventilation holes and wherein said second end cap actsto shield at least a portion of said second set of ventilation holes.25. A wind turbine comprising at least one wind turbine blade as claimedin claim
 1. 26. A method of manufacturing a wind turbine blade, themethod comprising the steps of: providing a wind turbine blade shell;providing a bulkhead located on or in said wind turbine blade; andproviding at least one pressure relief conduit as claimed in claim 1having conduit openings either side of said bulkhead, said pressurerelief conduit arranged to equalise the pressure difference across saidbulkhead.
 27. The method of claim 26, wherein said step of providing atleast one pressure relief conduit comprises providing a conduit whichextends through said bulkhead.
 28. The method of claim 26, wherein saidstep of providing at least one pressure relief conduit comprisesproviding a conduit which is located adjacent said bulkhead, preferablyextending through a sealant member or sealing flange provided around theperiphery of said bulkhead between said bulkhead and said wind turbineblade shell.
 29. The method of claim 26, wherein the method comprisesthe step of: embedding at least a portion of said pressure reliefconduit in a wall of said wind turbine blade shell, prior to a step ofinstalling said bulkhead in said wind turbine blade shell.
 30. Themethod of claim 29, wherein the step of providing a wind turbine bladeshell comprises the steps of laying up a fibre-based composite in amould and curing said fibre-based composite to form at least a portionof a wind turbine blade shell, and wherein said step of embeddingcomprises incorporating at least a portion of said conduit in said bladewall during said laying up process.
 31. The method of claim 26, whereinthe method comprises the steps of: securing said pressure relief conduitto an internal surface of said wind turbine blade shell, preferablyadhering said pressure relief conduit to said internal surface; andsealing said bulkhead in said wind turbine blade shell using a sealingflange about the periphery of said bulkhead, wherein said pressurerelief conduit extends either side of said sealing flange.